The hydroformylation of ethylenically unsaturated compounds to form alcohols is of considerable industrial importance. The process has been in commercial operation for decades and over the years much development work has been done to optimize the reaction conditions, the catalyst system, and the equipment. Although significant progress as regards higher yield and selectivity to the desired reaction products has been made, it is felt that in some aspects further improvement of the process is still needed.
Conventional modes of operation are based on the recovery of a cobalt carbonyl hydrocarbyl tert-phosphine complex by use of a recycle solution purge stream, as was disclosed in U.S. Pat. No. 3,418,351. According to such processes the contents of the reactor pass to a stripper where hydrogen, carbon monoxide, and the ethylenically unsaturated compound are vented to a recycle compressor and retuned to the reactor. The alcohol products are taken off overhead of the stripper and the bottom of the stripper is a solution of the catalyst complex and high-boiling byproducts, which are known as heavy ends. The bottom solution is recycled to the reactor, but to prevent build-up of heavy ends, at least a portion of this stream is subjected to a bleeding off process to separate the catalyst complex from the heavy ends. Unfortunately, this bleeding off procedure leads to a substantial loss of active catalyst, which cannot easily be separated completely from the heavy ends. Since the catalyst is the most expensive constituent of the process there is a need for a process preventing such loss of active catalyst complex.
The present invention provides a process that does not lead to substantial loss of catalyst during the recycle process and that prevents the formation of heavy ends as much as possible.